Minimizing or preventing the deposit of pitch in pulp and paper making processes is critical to minimizing equipment fouling and down time, maximizing production efficiency, and improving product quality. Pitch is composed of low molecular weight olephilic materials (primarily triglycerides, fatty acids, terpenes, resin acids and esters), which are released from wood fibers during chemical and mechanical pulping processes. This resinous substance usually precipitates as calcium and magnesium salts, causing problems with the wet end components of paper machines.
Known methods for pitch control include cationic fixation with alum or cationic polymers, dispersion with surfactants, absorption with talc, and chelation of heavy metals. Enzymatic methods also are known. For example, U.S. Pat. No. 5,176,796 to Irie, et al. discloses adding acylglycerol lipase to mechanical pulp paperstock or reuse water; U.S. Pat. No. 5,256,252 to Sarkar et al. discloses adding a lipase and a cationic polymer to a papermaking cellulosic slurry; and U.S. Pat. No. 5,667,634 to Fujita et al. discloses adding a water-soluble polyelectrolyte to increase the hydrolysis rate of esters in the presence of a lipase.
Effectively employing these and other pitch control methods, however, requires an accurate assessment of the quantity of depositable pitch present in the pulp and process waters throughout several points in the papermaking process. Standard diagnostic techniques for measuring pitch include a test to measure the total organic extractive content of the pulp. Unfortunately, known methods of triglyceride analysis of pulp take between about 8 and 24 hours to complete one set of samples. Therefore, the test results are useful only for post evaluation of the process system; they do not provide an assessment of the current state of the process, and yield unreliable and unfocused results. Accordingly, use of analytical methods to accurately apply pitch control measures is quite limited, as the dynamic nature of the pitch level in a continuous papermaking process requires a timely response by the pitch control measures. It would be highly advantageous to have a method that analyzes the triglyceride content of the pulp quickly and accurately so that process parameters can be adjusted to timely and accurately prevent pitch deposition problems.
One current method of triglyceride analysis is based on the analysis of fatty acids produced by the reaction of triglyceride hydrolysis in the presence of lipase:
Briefly, the method steps include (1) analyzing the fatty acid content of a first pulp sample that has not been treated with enzyme using an extraction, evaporation, and titration procedure; (2) calculating the percent of organic acid as oleic acid for the first sample; (3) treating a second pulp sample with a high dose of enzyme under conditions to ensure complete conversion of triglyceride to fatty acids and glycerol; (4) analyzing the fatty acid content of the enzyme-treated second pulp sample using the extraction, evaporation, and titration procedure; and (5) comparing the difference of organic acid in the first sample and the second sample. The triglyceride content is determined by the difference of fatty acid content before and after lipase treatment of the pulp sample, multiplied by a conversion factor. The conversion factor is the ratio of the molecular weight of the triglycerides to the molecular weight of the fatty acids. It is assumed that at high lipase dosage, the triglycerides are converted entirely to fatty acids and glycerol. No side reactions occur.
The extensive extraction, evaporation, and titration procedures required to assess fatty acid content are time consuming and labor intensive. For example, the fatty acids in the pulp sample are extracted into a hexane layer and aliquots of the hexane layer then are evaporated, leaving an organic residual that subsequently is dissolved into an aqueous isopropanol solution, which is then titrated with potassium hydroxide solutions using thymol blue as a pH indicator.
Another method also involves an extensive solvent extraction step followed by a high cost instrumental analysis step, involving high performance liquid chromatography (HPLC), thin layer chromatography (TLC), or gas chromatography (GC). These extraction-based methods typically take between about 8 and 24 hours to complete, require the use of potentially dangerous volatile organic compounds or toxic solvents, and are very labor intensive. The instrumental analysis is not portable for on site analysis, and the results often are inaccurate or irreproducible. It would be advantageous to have an accurate test method that does not require the extraction step, so that the pulp could be tested directly and rapidly. Such a test preferably would be portable, fast and easy to use, without high cost instrumental analysis. It would be beneficial if the method also minimized or eliminated the tester's potential exposure to volatile organic compounds or toxic solvents required by the extraction-based methods.
A further disadvantage of known methods is that pitch deposition does not correlate directly with the total organic extractive content of the pulp. Rather it is the pitch on the surface of the pulp fibers or in the suspension, i.e. the depositable pitch, that is the greatest concern in pitch deposition. Total pitch consists of pitch located on the surface of the fibers and pitch trapped within the pulp fibers. The pitch trapped within the fibers generally does not contribute to the pitch deposition problem, as it remains intact within the fibers and does not have a chance to react. The extraction-based analytical methods described above give the content of the total organic extractive chemicals in the pulp sample, which has no close correlation with the pitch deposition problems. Therefore, a test method providing results that directly correlate to pitch depositions problems would be highly beneficial.
It would be desirable to provide methods, devices, and kits for accurately and rapidly determining the depositable triglyceride content of a pulp sample, particularly for use in a continuous papermaking process. It would also be desirable to provide methods for enhancing the effectiveness of pitch control measures in a papermaking process based on such determinations. It would further be desirable to provide methods for measuring the surface triglycerides in wood pulp, wherein the test is portable, fast and easy to use without high cost instrumental analysis, and minimizes or eliminates the tester's potential exposure to volatile organic compounds or toxic solvents required by extraction-based total organic content diagnostic assays.